As the end of the year approaches, millions of travelers are reviewing their frequent-flier accounts to determine how many miles they have and what to do with those miles next year.

The airlines are doing a year-end review as well. In the past week, three have made major changes to their frequent-flier programs to make them more attractive to their best customers.

Some of the changes, such as those done by United Airlines and American Airlines, were applauded by frequent fliers. But some fliers see changes by Delta Air Lines as a means of forcing business travelers to purchase higher priced tickets.

Yesterday, United said members who are within 10,000 miles or 10 trips of reaching one of its top-tier elite levels can pay $25 to get three more months to qualify. Travelers have until Feb. 16 to register for the extension that expires March 31.

The higher the status, the more perks, such as free first-class upgrades, guaranteed seats on sold-out flights, and priority boarding and seating.

This past weekend, American Airlines offered a free three-month gold-level membership to select members of its frequent-flier program who didn't quite earn the required 25,000 miles this year. These travelers have until March 31 to fly 5,000 more miles to retain their gold status, which gives them free upgrades, a discount on airline club dues and bonus miles. Those travelers who are just shy of 50,000 miles -- platinum level -- were given three additional months to fly 10,000 more miles to obtain that status. American spokesman Tim Kincaid would not comment on how many of American's 43 million members received the incentives.

But Delta's move has sparked controversy. Last week, Delta Air Lines said it was reducing the number of miles a traveler would earn toward qualifying for elite levels if that traveler was flying on a deeply discounted ticket -- one that required a Saturday night stay or was bought weeks in advance.

As part of the change, business travelers who pay higher fares would get the full or even extra miles toward elite status. But those traveling on discounted tickets, even if they're flying the same number of miles as a full-fare traveler, would only receive half as many points. The changes go into effect Jan. 1 but won't begin to affect most of Delta's 32 million frequent fliers until 2004, said Jackie Yeaney, director of marketing and head of Delta's SkyMiles program.

Delta says its change will reward travelers who pay more by helping them earn elite status more quickly. "There are thousands of customers who will reach medallion class with these changes," Yeaney said.

Chris McGinnis, editor of TheTicket, a Delta frequent-flier newsletter, said the move would eventually shrink membership in Delta's top tiers, making it harder to get upgrades and free trips -- a major complaint among seasoned business travelers. But he also said the move "widens the gap between the rich and the poor," especially when many companies require their employees to fly on discounted tickets.

Rayshad Holmes of Washington has racked up more than 102,000 miles with Delta during the past two years. Holmes flies to Miami about seven times a year. But now he says those trips won't qualify him for elite status with Delta because his employer, the Foundation for Independent Higher Education, requires that he purchase cheaper, advance tickets.

"This is ridiculous. This is not how you build customer loyalty. I might as well go out to BWI and fly Southwest," Holmes said.

Jacqueline Hoell, a statistics professor at Georgetown University, said she feared she will lose her priority boarding status, which guarantees she can find some overhead space for her carry-on luggage before other passengers board. Hoell considered this the most valuable perk in Delta's program. Because she flies short trips on discounted tickets, Hoell said she was destined to lose her status.

"That's the one thing I treasure with flying Delta," she said. "They're punishing us for planning ahead. Delta doesn't have to be my airline of choice now."

Delta's Yeaney said the airline has received very few complaints about the changes. "We've been quite pleased with the response," she said.